Enzymes
What is an Enzyme?
An enzyme is a protein that speeds up chemical reactions in living things.
Enzymes are called catalysts because they speed up reactions without being used up.
Enzymes can be used over and over again.
Example: Catalase is an enzyme.
What is a Substrate?
A substrate is the substance an enzyme acts on.
The enzyme changes the substrate into new substances called products.
Example:
Enzyme: Catalase
Substrate: Hydrogen peroxide (H₂O₂)
Products: Water (H₂O) and Oxygen (O₂)
The Active Site
The active site is the place on an enzyme where the substrate attaches.
The substrate must fit the active site like a lock and key.
Only the correct substrate fits the enzyme.
Enzyme Reaction
Catalase Reaction:
2H₂O₂ → 2H₂O + O₂
Catalase breaks down hydrogen peroxide into:
Water
Oxygen gas
Why is Catalase Important?
Hydrogen peroxide is harmful to cells.
Catalase breaks it down into safe substances.
This helps protect living cells.
Factors That Affect Enzyme Activity
Temperature
Cold: Enzymes work slowly.
Warm (optimal temperature): Enzymes work the fastest.
Too Hot: Enzymes denature (lose their shape) and stop working.
pH
Every enzyme works best at a certain pH.
If the pH is too high or too low, the enzyme may not work properly.
Denaturation
Denaturation happens when an enzyme loses its shape.
High temperatures can cause denaturation.
A denatured enzyme cannot bind to its substrate.
Experimental Design
Independent Variable
The factor you change.
Example: Temperature
Dependent Variable
The factor you measure.
Example: Amount of oxygen produced (bubble height)
Controlled Variables
Things kept the same.
Amount of enzyme
Amount of substrate
Time
Equipment
Control Group
The normal group used for comparison.
Example: Room temperature
Reading a Graph
If enzyme activity is shown on a graph:
More bubbles = More oxygen = Higher enzyme activity
Fewer bubbles = Less oxygen = Lower enzyme activity
Usually:
Cold = Low activity
Warm = Highest activity
Hot = Low activity because the enzyme is denatured
Key Vocabulary
Word | Meaning |
Enzyme | Protein that speeds up chemical reactions |
Catalyst | Speeds up a reaction without being used up |
Substrate | Substance an enzyme acts on |
Active Site | Place where the substrate binds |
Product | Substance made after a reaction |
Catalase | Enzyme that breaks down hydrogen peroxide |
Hydrogen Peroxide | Substrate for catalase |
Denature | Lose shape and stop working |
Optimal Temperature | Temperature where an enzyme works best |
Test Tips
Enzymes are proteins.
Enzymes speed up chemical reactions.
Enzymes are not used up.
The substrate is what the enzyme acts on.
The active site is where the substrate fits.
Catalase breaks down hydrogen peroxide.
The products are water and oxygen.
Warm temperatures usually produce the highest enzyme activity.
High temperatures can denature enzymes.
A denatured enzyme cannot function properly.
Remember the lock-and-key model: only the correct substrate fits the enzyme.